The present invention relates to a method for forming a fine pattern and more particularly to a method for manufacturing the fine pattern used for forming a color LCD element used for a display unit such as an information terminal, a color filter used for a color image sensor and a color scanner, and a shading pattern filter 1 as well as the fine pattern used for an etching mask or a plating mask used in forming a high-density printed board built in a semiconductor packaging such as an IC card terminal and an electronic instrument such as a portable information terminal and a variety of printed boards such as a multi-layered printed board and a flexible printed board, the color filter and the shading pattern formed by the method, and the color LCD element and the printed board arranged to use the color filter.
As a conventional method for forming a fine pattern used for forming the color filter and the shading pattern filter used for a LCD element, for example, a pigment dispersing method has been realized where coloring pigment is fine dispersed in photo resist. For forming the fine pattern, the pigment dispersing method adopts a photolithograph technique often used for a semiconductor process. This pigment dispersing method, however, needs a process of coating photo resist and an exposure process for each wafer so that the method gives rise to an intricated manufacturing process and needs an expensive exposure device. Further, as a method for manufacturing the printed board, for example, the subtracting method and the additive method have been conventionally proposed. The subtracting method is arranged to form a predetermined insulating circuit pattern on a copper foil on the surface of a coppered substrate and then removing an unnecessary portion of the copper foil by an etching process with the circuit pattern as an etching mask, for forming wiring conductors. The additive method is arranged to apply catalyzer on the surface of an insulating substrate with no copper foil, form a predetermined insulating circuit pattern on the surface of the substrate, and forming wiring conductors by an electroless copper plating technique with the circuit pattern as a plating mask.
On the other hand, as a method for forming the insulating circuit pattern on the surface of the substrate, for example, a photolithograph method may be referred which is arranged to develop a photo resist by exposure. It is known that this method is often used in the semiconductor process. This photolithograph method provides an intricated manufacturing process because it needs processes of coating and exposing the photo resist on each layer. Further, various devices used by this method such as an ultraviolet exposing device are so costly that the resulting product manufactured by this lithography method is made expensive. To overcome these shortcomings, from various points of view, there have been studied various manufacturing methods with which the fine pattern can be manufactured more easily and at low cost and a precision of forming the fine pattern can be improved.
As an example, JP-A-61-233704 has disclosed a method for forming a fine pattern for the color filter. This method includes the steps of: exposing and developing resist containing pigment fine dispersed therein for forming a fine pattern on a surface of a peel layer made of organic polymer on a master substrate; and stripping the fine pattern off the master substrate and transferring the fine pattern on a media substrate with an adhesive imaging layer made of organic polymer by virtue of heat and pressure given by a laminator. This method, however, needs to keep the thermal expansion of the master substrate suitable to that of the media substrate since it utilizes heat and pressure for the stripping and transferring operation. This may degrade the fine pattern in transfer.
Likewise, as a method for forming a fine pattern used for the color filter, JP-A-63-266482 has disclosed the method taking the steps of: partially electrodepositing proper resin for each color for forming a fine pattern on an insulating master substrate having electrodes shaped to the form of the color filter; and bonding and pressurizing the fine pattern on the media substrate with adhesion of the resin itself for stripping and transferring the fine pattern. This method has a merit that the master substrate can be repetitively used. However, the strip and transfer of the fine pattern with the adhesion of the resin itself disadvantageously results in weakening bonding force of the resin with the media substrate, thereby being unable to completely stabilize the strip and transfer.
From the above-mentioned point of view, for more reliably stripping and transferring the fine pattern on the media substrate, a proposal has been made in JP-A-3-150376. This proposal for stripping and transferring the fine pattern concerns with a method which takes the steps of: forming a peel layer made of a releasable coating film on a master substrate; electrodepositing a fine pattern made of electrodeposit resin on the peel layer; and bonding and pressurizing the electrodeposit resin on a bonding layer formed on a media substrate. Further, a method dedicated to an etching mask has been disclosed in JP-A-4-260389. This method takes the steps of: forming a pattern of an electrodeposit adhesive agent on a fine pattern formed by the partial electrodeposition of the resin; mirror-processing a conductive layer where no masking layer is formed for giving rise to a peeling effect; and bonding and pressurizing the patterns onto a media substrate. This method for stripping and transferring the fine pattern on the media substrate therefore utilizes the adhesive characteristic of the electrodeposit agent pattern.
However, this conventional method for forming the fine pattern is disadvantageous in that the fine pattern cannot be completely stripped and transferred or misshaped when stripping and transferring the fine pattern from the master substrate to the media substrate, because the fine pattern made of the electrodeposit resin has strong bonding force to the master substrate. Moreover, since the fine pattern strongly bonded on the master substrate is forced to be stripped, this method gives a damage to the master substrate and thus shortens the repetitive usable duration of the master substrate.
On the other hand, the conventional LCD element is used for a display device of an information terminal such as a personal computer or a toy device such as a video game. In particular, the display device used in the portable information terminal or the toy device utilizes lots of LCD elements, because such devices are required to be reduced in size, weight and power consumption. As the display device keeps its displayed content more variable and its density higher, the demands for the LCD element, in particular, a color LCD element are going higher and higher year by year.
The conventional color LCD element is arranged to have a transparent substrate having a transparent pixel electrode formed thereon, a transparent substrate having a color filter and a transparent pixel electrode laminated thereon, and a liquid crystal material laid between both of the transparent substrates with their transparent pixel electrodes opposed to each other. Further, a deflection plate is located outside of each of the transparent substrates, so that a light source is provided in close proximity to one deflection plate.
The transparent substrate of the color LCD element has often used a glass substrate. Unfortunately, however, the glass substrate occupies a large weight ratio of the overall color LCD element and has difficulty in thinning. To reduce the LCD element in weight and thickness, the use of a plastic film substrate for the color LCD element is not being studied. For example, JP-A-61-149984 discloses the color LCD element which includes a plastic film substrate having a transparent pixel electrode formed thereon, another plastic film substrate having a transparent pixel electrode formed on one surface thereof and a color filter formed on the other surface thereof, and a liquid crystal material laid between both of the plastic film substrates with their transparent pixel electrode sides opposed to each other. Moreover, there are located deflection plates outside of the plastic film substrate and the color filter. A light source is provided in close proximity to the deflection plate located on the side of the color filter.
However, the plastic film substrate is so low in rigidity that the plastic film substrate on which the color filter is to be formed has difficulty in keeping its flatness excellent. When the pigment dispersing method is used for forming the color filter, the coating amount of resist containing the pigment fine dispersed therein is made so uneven that the film thickness of the color filter is distributive and the patterning precision of the color filter is made lower and thereby the precision with which the color filter is formed is lowered. As a result, this conventional method disclosed in JP-A-61-149984 has a disadvantage that the strength of the passing light is so uneven that color shading in a narrow range and brightness shading in a large range are brought about.
On the other hand, as mentioned earlier, the LCD element may have various types of light sources. For example, a transmission type LCD element that provides a light source such as a cold cathode fluorescent lamp on its rear portion, a reflection type LCD element that provides a reflection plate for reflecting an external ray incident to the rear portion of the LCD element, or a half-transmission type of LCD element that provides a half-transmission reflection plate and a light source such as an LED on the rear portion of the LCD element.
The transmission type LCD element uses a light source, so that it may be used in a dark place and thus provide a vivid image, while it has a large power consumption. This imposes restriction on an operating time of the display. To overcome this drawback, this LCD element is required to provide a large-volume battery, which leads to an obstacle to reducing a portable display in size. This holds true to the half-transmission type LCD element.
On the other hand, the reflection type LCD element does not include a light source, so that it does not consume electric power so much and can be operated for a far longer time than the transmission type or the half-transmission type LCD element. However, the reflection type LCD element disables to display the image unless the ambient light is incident to the LCD element. It means that this type LCD element cannot be used in a dark place. For example, therefore, if it is applied to a portable phone that is now under progressive prevailing, this type LCD element lacks in correspondence to an urgent condition such as a blackout. In addition, this type LCD element utilizes as a light source the light reflected on the rear portion, so that its light quantity is smaller than that of the transmission type LCD element. It means that the reflection type LCD element inevitably lowers its brightness and in particular degrades vividness of the colored display.
The present invention is made to overcome the foregoing disadvantages the prior art involves.
It is an object of the present invention to provide a method for manufacturing a fine pattern with which method a fine pattern formed on a master substrate is allowed to be completely stripped and transferred onto a media substrate without changing the shape of the fine pattern and with excellent reproducibility and with reliance, the repetitive use of the master substrate is made possible, and the high-definition and high-density fine pattern can be mass-produced with ease, and a color filter, a shading pattern filter and a printed board which are formed to have the high-definition and high-density fine patterns by the manufacturing method and is excellent in massproductivity and precision of forming the pattern.
It is a further object of the present invention to provide a color LCD element which utilizes the color filter and enables to offer a highly color reproducible image without color and brightness shadings.
It is a yet further object of the present invention to provide a color filter which keeps a color-emitting function for a certain limited interval later than when light from a light source or ambient light disappears and enables to offer a color-emitting function with high brightness and vividness even in the environment where a light volume is short, and a color LCD element provided with the color filter.